Polymers have conventionally been produced from crude oil of fossil origin. In recent times biopolymers made from renewable raw materials have increasingly been studied as an alternative. One such raw material is tall oil obtained as a byproduct from cellulosic pulp cooking process.
Tall oil contains fatty acids and resin acids, which can be subjected to catalytic hydrodeoxygenation (HDO) and cracking, yielding a hydrocarbon-bearing liquid product as well as gas and water. The liquid hydrocarbons have been turned to biofuels, but there is even literature on turning them to monomeric compounds, which can serve as starting materials for the production of polymers.
WO 2011/151528 describes catalytic hydrodeoxygenation of various tall oil materials, such as crude tall oil (CDO), distilled tall oil (DTO) or tall oil fatty acids (TOFA), followed by separation of suitable aromatic hydrocarbons such as p-xylene or o-xylene from the liquid product and oxidizing them to terephthalic acid useful for the production of polyethylene terephthalate of biologic origin (bio-PET).
WO 2010/086507 teaches a process for the production of polymerizable ethylene and propylene from a distilled mixture of at least 75% of tall oil fatty acids and no more than 25% of tall oil resin acids, which is subjected to catalytic deoxygenation with hydrogen, followed by subjecting the yield of liquid hydrocarbons to steam cracking, which yields said monomers.
In order to produce bio-based olefinic monomers such as ethylene or propylene by a simpler process and with increased yield it would be desirable to use crude tall oil as the starting material, instead of acids purified by distillation. The reason for purifying the acids has been the tendency of the impurities to poison the catalyst. Even the resin acids present in crude tall oil have been regarded as less desirable, producing aromatic hydrocarbons that could not be turned to polymerizable olefins by hydrocracking.